1. Field of the Invention
The present invention relates to plasma treatment for performing etching or the like on a substrate to be treated; and, more particularly, invention relates to a plasma treatment method and plasma treatment apparatus in which the treatment characteristics in the central part of the substrate and those in the peripheral part of the substrate to be treated are uniformized.
2. Related Background Art
Various methods have been devised for conventional plasma treatment apparatuses in order to uniformize the plasma density (ion current value) and ion energy (RF bias voltage) in the plane of a substrate (wafer) and to uniformize the substrate temperature. For example, the publication of Japanese unexamined patent No. 7-18438 discloses a technique for uniformizing the temperature distribution in the substrate by forming roughness on the surface of an insulating material on a substrate supporting face of a flat electrode, changing the density or depth of the rough surface of the insulating material, and distributing the electrostatic adsorption.
As the substrate size increases and the etching size becomes finer, however, the influence of the distribution of etching reaction products in the central part and those in the peripheral part of a substrate becomes tangible.
FIG. 15 is a diagram for explaining the behavior of etching reaction products. As shown in the diagram, etching reaction products such as Al, Cl, C, and the like react with a plasma etching gas (ions and radicals) on a substrate (wafer) 2 to be treated, evaporate in a vapor phase, and become Al2Cl6 or the like. The reaction products show complicated behavior such that they are directed again at the substrate 2 to be treated or they are dissociated again in the plasma and the dissociated species are directed at the substrate 2. That is, etched Al on the bottom of the substrate is released as reaction products into a vapor phase and a part of them is dissociated again in the plasma and is again directed at the substrate 2. A photo resist 25 is likewise etched so that the substrate is again irradiated with the reaction products of the resist. Electrically neutral species among the species dissociated from the reaction products in the plasma are directed also at the side walls of an area to be etched and are deposited. Such species, species which are obtained by etching the bottom face and directly deposited on the side walls, species directed at the side walls sputtered by the incident ions including physical or chemical elements, and the like are deposited, thereby forming a side wall protection layer 26.
Among them, with respect to the re-irradiation of the reaction products, non-uniformity of an irradiation amount in the plane of the substrate tends to occur by the following reason. The reaction products obtained by etching and released into a vapor phase are exhausted as a gas from the etching chamber. The outer the position of the substrate is, the more the reaction products are exhausted efficiently. As shown in FIG. 16, therefore, in the density distribution of the reaction products in the vapor phase, that is, the re-irradiation amount distribution of the reaction products, inevitably, the density or the re-irradiation amount is high in the central part of the substrate and is low in a peripheral part.
As mentioned above, in a peripheral part of the substrate, the amount of the reaction products is smaller than that in the central part of the substrate since they are exhausted together with an etching gas. In case of metal etching, if the side wall protection layer is thick, the etch rate on the side walls by the ion assisted reaction becomes low. Because of this, when describing a process for a trench as an example, the shape of a part to be etched becomes a so-called tapered shape in which the width is reduced as the etch depth increases. On the contrary, when the side wall protection layer is too thin, the side walls are etched and the part to be etched becomes wider than a target width. Consequently, in order to obtain a vertical shape as an etched part, the amount of deposition of the side wall protection layer has to be optimized so as to obtain a proper thickness and prevent the side walls from becoming fat or thin.
On the other hand, with reduction in the etching size, the need for the processing accuracy of dimensions increases. For example, when about {fraction (1/10)} of a design dimension is a permissible level, the permissible level is xc2x10.05 xcexcm for the design dimension of 0.5 xcexcm. With reduction in the dimension to 0.25 xcexcm and 0.13 xcexcm, the permissible levels become xc2x10.025 xcexcm and xc2x10.013 xcexcm, respectively. In order to achieve such a required specification, factors exerting an influence on the processing dimension have to be made clear and controlled.
With the reduction in the etching size, also in dense and sparse patterns in which fine patterns and sparse patterns which are not so dense mixedly exist, the need for the processing accuracy of dimensions has been increasing.
It is an object of the present invention to provide plasma treatment method and apparatus in which an influence on treatment characteristics of reaction products in a plasma treatment such as etching is offset and uniform treatment characteristics can be obtained in the plane of a substrate.
It is another object of the present invention to provide plasma treatment method and apparatus which improves the uniformity in the substrate plane of a shape to be processed in consideration of influences of reaction products at the time of plasma treatment such as etching.
It is further another object of the present invention to provide a plasma treatment method and a plasma treatment apparatus which can obtain an etching treatment characteristic such that there is no variation in processing dimension in dense and sparse patterns.
According to a feature of the invention, in a plasma treatment method of performing etch treatment to a substrate to be processed by using a gas plasma via a mask in a treatment chamber, plasma treatment is performed while maintaining the in-plane uniformity of a side wall protection layer formed on the side walls of a part to be etched in the substrate.
According to another feature of the invention, in a plasma treatment method of treating a substrate to be processed by using a gas plasma via a mask in a treatment chamber, plasma treatment is performed while equalizing an amount of deposition of a side wall protection layer formed on the substrate to be processed in the center of the substrate and that in an end part of the substrate, and maintaining the in-plane uniformity of the side wall protection layer.
According to further another feature of the invention, in a plasma treatment method of treating a substrate to be processed with a gas plasma by using a resist as a mask in a treatment chamber, plasma treatment is performed to the substrate while maintaining the uniformity of a deposition amount of reaction products which are generated by a reaction between the substrate to be processed and the plasma and are directed at and deposited on the substrate in the plane of the substrate to be processed, thereby forming a side wall protection layer having a uniform plane on the substrate.
According to another feature of the invention, in a plasma treatment method of performing plasma treatment to a substrate to be processed with a gas plasma by using a resist as a mask in a treatment chamber, the plasma treatment is performed while maintaining the in-plane uniformity of a side wall protection layer formed on the substrate by controlling the temperature of the substrate.
It is another feature of the invention that the plasma treatment is performed to the substrate to be processed while adjusting the pressure, flow rate, and mixing ratio of a process gas in the treatment chamber.
It is another feature of the invention that the plasma treatment is performed to the substrate to be processed while regulating an exhaust amount of the reaction products from the treatment chamber.
It is another feature of the invention that the plasma treatment is performed to the substrate to be processed while adjusting the kind of the process gas or the pressure of the process gas in the treatment chamber.
It is another feature of the invention that variation in a deposition amount of reaction products in the plane of the substrate to be processed is maintained within xc2x110%.
It is another feature of the invention that the diameter of the substrate to be processed is 200 mm or larger and a pattern formed on the substrate to be processed is 0.35 xcexcm or smaller.
According to another feature of the invention, in a plasma treatment apparatus for treating a substrate to be processed by using a gas plasma, a substrate holding electrode on which the substrate to be processed is placed and which controls the temperature of the substrate so that temperatures in the central and peripheral parts of the substrate are different Ad and has a function of maintaining in-plane uniformity of a deposition amount of reaction products in the plane of the substrate.
In case of etching, usually, it is requested to perform etching vertically and faithfully to the processing dimension via a mask. In this case, etching in the direction vertical to the etching direction, that is, etching of the side walls exerts an influence on the processing dimension. In the etching of the side walls, when the etch pressure is high, injected ions also contribute to the etching. When the etch pressure is sufficiently low, the ion injection can be almost ignored. In such a state where the ion injection can be almost ignored, the etching of the side walls largely depends on a chemical reaction between the side walls and radicals. The chemical reaction depends on the temperature and the density and kind of radicals irradiated and deposited. In case of etching, reaction products which suppress the chemical reaction are deposited on the side walls. It can be said that the amount of the deposition, that is, the thickness of the side wall protection layer decides the side wall etch rate. In other words, the control of the thickness of the side wall protection layer is the key to improve the processing accuracy.
Consequently, in the etching of the finer pattern on which the influence of the reaction products is large, especially, it is necessary to consider distribution characteristics such that the reaction products in the vapor phase are not uniform in the plane of the substrate and the amount of the reaction products is smaller in the peripheral part of the substrate, and to obtain a plasma distribution and a substrate temperature distribution which make the in-plane distribution of the side wall protection layer uniform by offsetting the influence.
According to the invention, in a plasma treatment method of treating a substrate to be processed with a gas plasma via a mask in a treatment chamber, the substrate is subjected to plasma treatment while maintaining the in-plane uniformity of the side wall protection layer formed on the substrate. By maintaining the in-plane uniformity of the side wall protection layer on the substrate to be processed, etch rate of the side walls by an ion assisted reaction becomes uniform. Even in case of a fine pattern, a vertical shape of the etched part can be easily obtained.
In order to maintain the in-plane uniformity of the side wall protection layer formed on the substrate to be processed, for example, the temperature distribution in the substrate plane is controlled. The higher the substrate temperature is, the lower the probability that the reaction products which are directed again at the substrate are deposited on the side walls of the part to be etched or the like is. That is, when the substrate temperature is constant, the deposition probability of the reaction products in the plane of the substrate becomes constant. Consequently, the amount of deposition on the side walls of the treated part, that is, the thickness of the side wall protection layer is proportional to the re-irradiation amount of the reaction products. As a result, the deposition amount of reaction products on the substrate increases in the center of the substrate and the shape of the treated part and that of a peripheral part become different.
In order to solve the problem and maintain the in-plane uniformity of the side wall protection layer on the substrate to be processed, at the time of the plasma treatment, for example, it is controlled so that the temperature in the center of the substrate is higher as compared with that in the peripheral part. Since the deposition probability of the reaction products is low when the temperature in the center of the substrate is high, even if the re-irradiation amount of the reaction products is large, the amount of reaction products deposited on the side walls of the etched part is therefore small. The temperature of the substrate is regulated to have a characteristic such that the temperatures in and out of the substrate plane are different so that the deposition amount of the reaction products to the side walls in the substrate plane becomes uniform. Thus, the treatment characteristics in the substrate plane can be made uniform.
When the substrate temperature is changed, not only the deposition probability of the reaction products changes but also the deposition probability of the etching gas plasma (especially, radicals) changes. The rate of etch reaction itself also changes. Consequently, since the generation amount of the reaction products changes, it is necessary to control the substrate temperature distribution in accordance with the conditions of plasma treatment such as etching.
For maintaining the uniformity in the plane of the side wall protection layer, there are various methods of controlling the temperature distribution in the substrate plane. For example, the surface of the electrode is divided into a part which comes into contact with the back face of the wafer and a part (trenches) which does not come into contact with the back face, and the in-plane temperature of the wafer can be controlled by utilizing the fact that the overall heat transfer coefficient in the contact part and that in the trenches are different. The overall heat transfer coefficient can be also changed by varying the depth of the trenches.
Further, the overall heat transfer coefficient can be controlled by coating the trench with a film. Further, by adjusting the kind and thickness of the film coated on the trench, the temperature can be changed according to a process. By coating with a film, cleaning can be made easily. The film does not have to be made of plastics but can be made of a metal or ceramics. The film has to be thin. The temperature of the wafer can be also controlled by coating a part which is in contact with the back face of the wafer with the film.
According to the invention, the plasma treatment method and the plasma treatment apparatus in which the influence on the etching characteristics of the reaction products in the plasma treatment is offset and the uniform treatment characteristics can be obtained in the substrate plane can be provided.